QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Yue-Wen Fang on August 31, 2015, 17:29

Title: transmission coefficient and conductence
Post by: Yue-Wen Fang on August 31, 2015, 17:29: Dear all,

I calculated two tunnelling states withe the corresponding sum transmission coefficient at the Fermi level without applying bias which are shown in the attachment. As shown in First-state.png and second-state.png, could I conclude that the second state has better conductance than that in the first state based on Landauer formula g=(e^2/h)T? What physics could I get from the two pictures?

Thank you in advance.
Title: Re: transmission coefficient and conductence
Post by: Jess Wellendorff on September 2, 2015, 11:56: What you have in those two figures are k-space resolved transmission spectra. Would you say that conductance is related to the integral transmission in all of k-space, or do you expect conductance only in specific (k_A, k_B) points in k-space? If the former, it's hard to say from a quick look at the pictures which displays the highest conductance.
Title: Re: transmission coefficient and conductence
Post by: Yue-Wen Fang on September 2, 2015, 15:37: Hi, Prof. Jess Wellendorff

Thanks for all your responses. When I posted this question, I thought transmission T in the Landauer formalism was just the max values shown in the color bar in the figures. But after reading some related reference papers and your reply, I feel I was wrong. T should be the integral transmission in BZ as you said.

Thanks again!
Title: Re: transmission coefficient and conductence
Post by: Yue-Wen Fang on September 3, 2015, 14:48: Quote from: Jess Wellendorff on September 2, 2015, 11:56
What you have in those two figures are k-space resolved transmission spectra. Would you say that conductance is related to the integral transmission in all of k-space, or do you expect conductance only in specific (k_A, k_B) points in k-space? If the former, it's hard to say from a quick look at the pictures which displays the highest conductance.

Besides, I want to calculate the complex band structures for the materials. For a junction, e.g. Fe/MgO(001)/Fe MTJ, do I need to convert the device configuration of Fe/MgO/Fe into bulk configuration, and remove the Fe atoms to calculate the complex band structures? From the official example for Si(100), it seems that we need to cleave the surfaces. For MgO, do I need cleave the (001) surface?

Thanks again.
Title: Re: transmission coefficient and conductence
Post by: zh on September 4, 2015, 12:11: To calculate the complex band structure of whole Fe/MgO(001)/Fe MTJ, you may convert the atomic structure into a bulk configuration.

For the MgO(001) case, you need to cleave the surface and make it without vacuum layer.
Title: Re: transmission coefficient and conductence
Post by: Yue-Wen Fang on September 4, 2015, 19:54: Hi, Prof. zh,

Thank you for your kind reply!

If I want to compare the conductance of for parallel configurations and anti-parallel configurations of Fe/MgO/Fe MTJ from the view of complex band, do you mean that I just need convert the device configurations into bulk configurations and further make a complex band structure calculation for the Fe/MgO/Fe superlattice (bulk configurations)?

Thanks!
Title: Re: transmission coefficient and conductence
Post by: Yue-Wen Fang on September 5, 2015, 15:36: Quote from: zh on September 4, 2015, 12:11
To calculate the complex band structure of whole Fe/MgO(001)/Fe MTJ, you may convert the atomic structure into a bulk configuration.

For the MgO(001) case, you need to cleave the surface and make it without vacuum layer.

In addition, do I need to set very dense k grid along c-axis (transport direction) as do in the transmission calculations?

Bests
Fang
Title: Re: transmission coefficient and conductence
Post by: zh on September 6, 2015, 12:25: Yes, you should use dense k-grid.
Title: Re: transmission coefficient and conductence
Post by: Yue-Wen Fang on September 6, 2015, 13:58: Prof. zh,

Thanks for your kind assistance.